OBSERVATIONS ON THE DUCTLESS GLANDS, THE SERUM CALCIUM, AND EGG-LAYING IN THE FOWL

¹ Rowett Research Institute, and the Physiological Department, the University, Aberdeen

In the yearly life-cycle of the fowl the serum calcium approximates the mammalian level during the growth period. As the first ovum develops in the ovary the calcium rises rapidly, reaching a maximum level with an average of from 10-30 grm. The calcium then falls relatively slightly for egg weight above 30 grm. until the egg is laid, when these changes begin again. Associated with these there are distinct histological alterations in the parathyroids. Parathormone raises the blood calcium of hens in the growth period, but has no effect during moulting, or on the blood calcium of cocks.

A supply of Ca in the diet sufficient only for maintenance does not permit of egg-laying.

The yearly cycle does not affect the structure of the pituitary, thymus, or adrenals. Seasonal variations in the size, structure and iodine content of the thyroid were confirmed.

I wish to express my acknowledgements to Dr ORR, who suggested the investigation, to Professor MACLEOD and Dr MAGEE for assistance and criticism, and to Professor SHENNAN for the photograph.